An electron beam emission device refers to a device for performing various processing, such as melting or reforming of a surface of a processed product, by emitting electrons by using high energy, and recently, the electron beam emission device is applied to various processing device fields in addition to an image display means or a non-destructive inspection device.
In general, as the electron beam emission device, a thermal type electron beam emission device, which emits electron beams by applying high voltage and high current to a filament, is used, but there are difficulties in maintaining a high degree of vacuum and manufacturing the filament, which directly causes problems with maintenance of the device.
Meanwhile, a cold type electron beam emission device, which is contrasted with the thermal type electron beam emission device, has been introduced. Various types of the cold type electron beam emission device have also been introduced.
FIG. 1 is a view illustrating an electron beam emission device using a concave cathode among the cold type electron beam emission devices.
As illustrated in FIG. 1, an electron beam emission device in the related art may include a cathode 20, an anode 30, an insulation unit 40, and a tube 50.
The cathode 20 is disposed at one end of the tube 50, and a downward surface of the cathode 20 has a gradient so as to be concave.
Further, the anode 30 is disposed at the other end in the tube 50, and disposed to be spaced apart from the cathode 20.
The cathode 20 is fixed to the tube 50 by the insulation unit 40, and a drive unit 60 for controlling electrical energy applied to the cathode 20 and a cooling unit 70 for cooling the cathode 20 are provided outside the insulation unit 40.
Meanwhile, the tube 50 is made of a quartz material which enables an internal state to be observed, withstands a high temperature, and enables insulation.
In addition, a focusing unit 80 and a deflecting unit 90 are installed at a lower side of the anode 30, thereby focusing and deflecting the emitted electron beams.
Therefore, the electrons emitted from the cathode 20 may form the electron beams while being accelerated and emitted by the anode 30, and may be focused while passing through the focusing unit 80, and an emission direction of the electrons may be deflected while the electrons pass through the deflecting unit 90.
However, the aforementioned electron beam emission device in the related art has the following problems.
First, because a rim 22 of the cathode 20 is formed in the form of a pointed end as illustrated in FIG. 2, an arc is generated at the rim 22 of the cathode 20 when high energy is applied such that the electron beam emission device 10 operates unstably, and as a result, there is a limitation in increasing an output.
Second, since a tube made of a quartz material is used as the tube 50, there is a problem in that the tube 50 is easily damaged due to impact applied when the device operates and repeated thermal shock.
Third, in a case in which metal is processed as a processing object to be processed by the electron beam emission device 10, metal vapor (fume) vaporized by the electron beams may be adhered and deposited on the tube, and the deposited metal vapor generates an arc when the electron beam emission device operates, and thus acts as a factor that limits use duration time of the tube.
Fourth, radioactive rays such as X-rays, which are harmful to a human body, may be generated when the electrons are reflected by the anode 30, but the tube made of a quartz material cannot block the radioactive rays, and as a result, there is a problem in that an environment harmful to an operator may be made.
Fifth, some of the electron beams emitted from the cathode 20 are not directed toward the anode, and may form backscattered electrons (BSE) that are directed in other directions.
Further, secondary electrons 9 may be emitted as elements such as nitrogen in the tube 50 collide with the accelerated electrons, and the secondary electrons 9 are scattered without being focused in comparison with the electron beams emitted from the cathode 20, and may be reflected in the tube 50 without passing through the anode 30.
In the following description, both of the backscattered electron and the secondary electron are referred to as a reflection electron.
Even though the reflection electron 9 does not have high energy, the reflection electron 9 may become a factor that serves to increase a temperature in the tube 50 by being reflected in the tube 50, or hinders a stable operation while generating an arc.